The invention relates to a device for pressure-based load detection, such as a device for determining the air mass flowing into the cylinder combustion chamber of an internal combustion engine cylinder in a motor vehicle.
Load detection involves the determination of the air mass, which for the purpose of combustion is drawn into the combustion chamber of a cylinder of an internal combustion engine.
There are two types of methods of load detection: (1) methods based on direct measurement of the air mass by a sensor system (for example, hot film air flow sensors, hot wire air flow sensors, or the like); and (2) methods which operate without direct air flow measurement. Methods having direct air flow measurement measure the air mass flowing into the intake manifold and calculate the air mass flowing from the intake manifold into the cylinder using a calculation model which describes the intake manifold dynamics. Methods without direct air flow measurement usually use the measured intake manifold pressure, from which a conclusion is drawn concerning the inflowing air mass by use of an air flow model. These methods are also referred to as pressure-based or intake manifold pressure-based methods for load detection. In intake manifold pressure-based methods for load detection, the air mass is determined as a function of the intake manifold pressure and the temperature of the air in the intake manifold. To allow conclusions to be drawn concerning the air flowing into the combustion chamber on the basis of the intake manifold pressure, complex calculation models are necessary which describe the fresh air mass flow from the collector in the intake duct into the combustion chamber of the cylinders. Parameters to be taken into account include the engine speed, the camshaft position, and the control times and/or stroke positions of exhaust and intake valves, the engine temperature, and for supercharged engines, the position of the bypass (wastegate). The fresh air mass remaining in the cylinders constantly increases with increasing intake manifold pressure for otherwise equal input variables (parameters) (see, for example, FIG. 2).
Known devices for pressure-based determination of the air mass (load) include intake manifold pressure sensors which are able to cover, i.e., measure, the entire intake manifold pressure range.
One aspect of the present invention provides a device which ensures improved accuracy in load detection, particularly in low-load regions.
The invention is based on the finding that as the result of the tolerance limits of the sensors, measurement errors occur that have various effects in the different load regions. A distinction is made between an absolute measurement error, whose proportion (magnitude) is constant over the entire measurement range and which corresponds to a percentage of the end value, and a relative measurement error, whose proportion varies as a function of the magnitude of the measured value. The relative measurement error increases disproportionately at low intake manifold pressures (loads), and in this specific case has a particularly disadvantageous effect on the accuracy of the load signal. However, it is precisely at low loads that high accuracy of the load signal is extremely important for drivability of a motor vehicle (for example, in the transition from high loads to idle). The larger the measurement range of a sensor and the higher the gradient of the load as a result of the intake manifold pressure, the more pronounced is the described disadvantageous effect. For these reasons, load calculation models for direct-injection supercharged engines are sensitive to pressure sensor tolerances that are present. For these engines, due to high valve overlap (i.e., phases in which the intake as well as the exhaust valves are open) and the intake manifold pressure range to be detected or measured, the gradient is twice as high as for non-supercharged engines. Thus, the device according to the invention is particularly suited for direct-injection supercharged internal combustion engines.
Exemplary embodiments of the present invention provide a device for determining the air mass flowing into the cylinder combustion chamber of an internal combustion engine cylinder in a motor vehicle, where the inflowing air mass may be determined by use of a calculation model for load detection as a function of the intake manifold pressure. A sensor device is provided for direct detection of the intake manifold pressure, having a measurement range so that by use of the sensor device the intake manifold pressure may be measured only in a lower partial range of the intake manifold pressure in the internal combustion engine. A calculation model is provided for indirect detection of the intake manifold pressure which is designed so as to be capable of determining by calculation the intake manifold pressure in an upper partial range of the intake manifold pressure in the internal combustion engine. The device is designed in such a way that within the lower partial range of the intake manifold pressure the inflowing air mass is determined as a function of the intake manifold pressure measured by the sensor device, and that within the upper partial range of the intake manifold pressure the inflowing air mass is determined on the basis of the intake manifold pressure determined using the calculation model.
One device according to the invention comprises a sensor device (intake manifold pressure sensor) whose measurement range covers only the lower portion of the physical intake manifold pressure range for the internal combustion engine. On account of the smaller measurement range, the absolute measurement error is less than for a measuring device which covers the entire physical measurement range (total physical intake manifold pressure range). In addition, because of the smaller relative measurement error, the error in determining the load as a function of the measured intake manifold pressure is much less at lower loads. Outside the pressure range of the pressure sensor used, the intake manifold pressure is determined by use of a calculation model, and the required load is computed based on the calculated intake manifold pressure. The error present due to the calculation model for calculating the intake manifold pressure in the upper range of the intake manifold pressure is much less noticeable, so that the advantages of increased accuracy clearly predominate in the lower range of the intake manifold pressure.
In one exemplary embodiment, the intake manifold pressure (value) measured in the lower portion of the intake manifold pressure range is directly used as an input variable for a load detection model for determining the load. Alternatively, the intake manifold pressure may be simulated over the entire intake manifold pressure range by use of a calculation model, whereby in the lower partial range of the intake manifold pressure (in which the intake manifold pressure is detected using a sensor device) the measured intake manifold pressure is sent to a control device, by means of which the modeled intake manifold pressure is matched to the measured intake manifold pressure.
According to one aspect of the present invention for supercharged engines, the sensor device is designed in such a way that the sensor device covers the entire intake manifold pressure range without an active supercharger device (thus, in this lower pressure range the intake manifold pressure is determined directly by measurement), whereas in the pressure range above the maximum intake manifold pressure without an active supercharger device the intake manifold pressure is determined up to the maximum intake manifold pressure with an active supercharger device by use of a model.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.